I reproduced the problem. It seems that mirrorlist.centos.org has problems with ipv6.
See using ipv6:
# curl -L 'http://mirrorlist.centos.org/?release=6.7&arch=x86_64&repo=updates'
Invalid release
Forcing ipv4:
# curl -4 -L 'http://mirrorlist.centos.org/?release=6.7&arch=x86_64&repo=updates'
http://mirror.cov.ukservers.com/centos/6.7/updates/x86_64/
http://mirror.ukhost4u.com/centos/6.7/updates/x86_64/